Cardioverter-Defibrillator Having a Focused Shocking Area and Orientation Thereof

ABSTRACT

One embodiment of the present invention provides an implantable cardioverter defibrillator for subcutaneous positioning between the third rib and the twelfth rib within a patient, the implantable cardioverter-defibrillator including a housing; an electrical circuit located within the housing; a first electrode coupled to the electrical circuit and located on the housing; and a second electrode coupled to the electrical circuit. Some embodiments also include a physiologic sensor. Other embodiments comprise methods of implanting and subcutaneously positioning an implantable defibrillator.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/901,333, filed Oct. 8, 2010 and published as US Patent ApplicationPublication Number 2011-0029032, which is a continuation of U.S. patentapplication Ser. No. 11/349,326, filed Feb. 6, 2006 and now U.S. Pat.No. 7,813,797; which is a continuation of U.S. patent application Ser.No. 10/011,947, filed Nov. 5, 2001 and now U.S. Pat. No. 7,039,459;which is a continuation-in-part of U.S. patent application Ser. No.09/940,273, filed Aug. 27, 2001 and now U.S. Pat. No. 7,069,080; whichis a continuation-in-part of U.S. patent application Ser. No.09/663,607, filed Sep. 18, 2000, now U.S. Pat. No. 6,721,597 and U.S.patent application Ser. No. 09/663,606, filed Sep. 18, 2000, now U.S.Pat. No. 6,647,292; the entire disclosures of which are all incorporatedherein by reference.

BACKGROUND

Defibrillation/cardioversion is a technique employed to counterarrhythmic heart conditions including some tachycardias in the atriaand/or ventricles. Typically, electrodes are employed to stimulate theheart with electrical impulses or shocks, of a magnitude substantiallygreater than pulses used in cardiac pacing. Shocks used fordefibrillation therapy can comprise a biphasic truncated exponentialwaveform. As for pacing, a constant current density is desired to reduceor eliminate variability due to the electrode/tissue interface.

Defibrillation/cardioversion systems include body implantable electrodesthat are connected to a hermetically sealed container housing theelectronics, battery supply and capacitors. The entire system isreferred to as implantable cardioverter/defibrillators (ICDs). Theelectrodes used in ICDs can be in the form of patches applied directlyto epicardial tissue, or, more commonly, are on the distal regions ofsmall cylindrical insulated catheters that typically enter thesubclavian venous system, pass through the superior vena cava and, intoone or more endocardial areas of the heart. Such electrode systems arecalled intravascular or transvenous electrodes. U.S. Pat. Nos.4,603,705; 4,693,253; 4,944,300; and 5,105,810, the disclosures of whichare all incorporated herein by reference, disclose intravascular ortransvenous electrodes, employed either alone, in combination with otherintravascular or transvenous electrodes, or in combination with anepicardial patch or subcutaneous electrodes. Compliant epicardialdefibrillator electrodes are disclosed in U.S. Pat. Nos. 4,567,900 and5,618,287, the disclosures of which are incorporated herein byreference. A sensing epicardial electrode configuration is disclosed inU.S. Pat. No. 5,476,503, the disclosure of which is incorporated hereinby reference.

In addition to epicardial and transvenous electrodes, subcutaneouselectrode systems have also been developed. For example, U.S. Pat. Nos.5,342,407 and 5,603,732, the disclosures of which are incorporatedherein by reference, teach the use of a pulse monitor/generatorsurgically implanted into the abdomen and subcutaneous electrodesimplanted in the thorax. This system is far more complicated to use thancurrent ICD systems using transvenous lead systems together with anactive can electrode and therefore it has no practical use. It has infact never been used because of the surgical difficulty of applying sucha device (3 incisions), the impractical abdominal location of thegenerator and the electrically poor sensing and defibrillation aspectsof such a system.

Recent efforts to improve the efficiency of ICDs have led manufacturersto produce ICDs which are small enough to be implanted in the pectoralregion. In addition, advances in circuit design have enabled the housingof the ICD to form a subcutaneous electrode. Some examples of ICDs inwhich the housing of the ICD serves as an optional additional electrodeare described in U.S. Pat. Nos. 5,133,353; 5,261,400; 5,620,477; and5,658,321, the disclosures of which are incorporated herein byreference.

ICDs are now an established therapy for the management of lifethreatening cardiac rhythm disorders, primarily ventricular fibrillation(V-Fib). ICDs are very effective at treating V-Fib, but are therapiesthat still require significant surgery.

As ICD therapy becomes more prophylactic in nature and used inprogressively less ill individuals, especially children at risk ofcardiac arrest, the requirement of ICD therapy to use intravenouscatheters and transvenous leads is an impediment to very long termmanagement as most individuals will begin to develop complicationsrelated to lead system malfunction sometime in the 5-10 year time frame,often earlier. In addition, chronic transvenous lead systems, theirreimplantation and removals, can damage major cardiovascular venoussystems and the tricuspid valve, as well as result in life threateningperforations of the great vessels and heart. Consequently, use oftransvenous lead systems, despite their many advantages, are not withouttheir chronic patient management limitations in those with lifeexpectancies of >5 years. The problem of lead complications is evengreater in children where body growth can substantially altertransvenous lead function and lead to additional cardiovascular problemsand revisions. Moreover, transvenous ICD systems also increase cost andrequire specialized interventional rooms and equipment as well asspecial skill for insertion. These systems are typically implanted bycardiac electrophysiologists who have had a great deal of extratraining.

In addition to the background related to ICD therapy, the presentinvention requires a brief understanding of a related therapy, theautomatic external defibrillator (AED). AEDs employ the use of cutaneouspatch electrodes, rather than implantable lead systems, to effectdefibrillation under the direction of a bystander user who treats thepatient suffering from V-Fib with a portable device containing thenecessary electronics and power supply that allows defibrillation. AEDscan be nearly as effective as an ICD for defibrillation if applied tothe victim of ventricular fibrillation promptly, i.e., within 2 to 3minutes of the onset of the ventricular fibrillation.

AED therapy has great appeal as a tool for diminishing the risk of deathin public venues such as in air flight. However, an AED must be used byanother individual, not the person suffering from the potential fatalrhythm. It is more of a public health tool than a patient-specific toollike an ICD. Because >75% of cardiac arrests occur in the home, and overhalf occur in the bedroom, patients at risk of cardiac arrest are oftenalone or asleep and can not be helped in time with an AED. Moreover, itssuccess depends to a reasonable degree on an acceptable level of skilland calm by the bystander user.

What is needed therefore, especially for children and for prophylacticlong term use for those at risk of cardiac arrest, is a combination ofthe two forms of therapy which would provide prompt and near-certaindefibrillation, like an ICD, but without the long-term adverse sequelaeof a transvenous lead system while simultaneously using most of thesimpler and lower cost technology of an AED. What is also needed is acardioverter/defibrillator that is of simple design and can becomfortably implanted in a patient for many years.

SUMMARY

One embodiment of the present invention provides an implantablecardioverter defibrillator for subcutaneous positioning between thethird rib and the twelfth rib within a patient, the implantablecardioverter-defibrillator including a housing; an electrical circuitlocated within the housing; a first electrode coupled to the electricalcircuit and located on the housing; and a second electrode coupled tothe electrical circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is now made tothe drawings where like numerals represent similar objects throughoutthe Figures where:

FIG. 1 is a schematic view of a Subcutaneous ICD (S-ICD) of the presentinvention;

FIG. 2 is a schematic view of an alternate embodiment of a subcutaneouselectrode of the present invention;

FIG. 3 is a schematic view of an alternate embodiment of a subcutaneouselectrode of the present invention;

FIG. 4 is a schematic view of the S-ICD and lead of FIG. 1subcutaneously implanted in the thorax of a patient;

FIG. 5 is a schematic view of the S-ICD and lead of FIG. 2subcutaneously implanted in an alternate location within the thorax of apatient;

FIG. 6 is a schematic view of the S-ICD and lead of FIG. 3subcutaneously implanted in the thorax of a patient;

FIG. 7 is a schematic view of the method of making a subcutaneous pathfrom the preferred incision and housing implantation point to atermination point for locating a subcutaneous electrode of the presentinvention;

FIG. 8 is a schematic view of an introducer set for performing themethod of lead insertion of any of the described embodiments;

FIG. 9 is a schematic view of an alternative S-ICD of the presentinvention illustrating a lead subcutaneously and serpiginously implantedin the thorax of a patient for use particularly in children;

FIG. 10 is a schematic view of an alternate embodiment of an S-ICD ofthe present invention;

FIG. 11 is a schematic view of the S-ICD of FIG. 10 subcutaneouslyimplanted in the thorax of a patient;

FIG. 12 is a schematic view of yet a further embodiment where thecanister of the S-ICD of the present invention is shaped to beparticularly useful in placing subcutaneously adjacent and parallel to arib of a patient;

FIG. 13 is a schematic of a different embodiment where the canister ofthe S-ICD of the present invention is shaped to be particularly usefulin placing subcutaneously adjacent and parallel to a rib of a patient;

FIG. 14 is a schematic view of a Unitary Subcutaneous ICD (US-ICD) ofthe present invention;

FIG. 15 is a schematic view of the US-ICD subcutaneously implanted inthe thorax of a patient;

FIG. 16 is a schematic view of the method of making a subcutaneous pathfrom the preferred incision for implanting the US-ICD;

FIG. 17 is a schematic view of an introducer for performing the methodof US-ICD implantation;

FIG. 18 is an exploded schematic view of an alternate embodiment of thepresent invention with a plug-in portion that contains operationalcircuitry and means for generating cardioversion/defibrillation shockwaves;

FIG. 19 is a top perspective view of an alternative S-ICD canister ofthe present invention depicting the top side of the canister housing anda lead electrode coupled to the S-ICD canister;

FIG. 20 is an exploded bottom perspective view of the S-ICD canister ofFIG. 19 showing an electrode in the shape of a thumbnail positioned onthe bottom surface of the canister housing;

FIG. 21 is a front elevational view of the S-ICD canister of FIG. 19depicting the curved canister housing;

FIG. 22 is a partial schematic view of the S-ICD canister of the presentinvention implanted subcutaneously in the thorax of the recipientpatient;

FIG. 23A is a top plan view of an alternative S-ICD canister of thepresent invention having a duckbill-shaped end to the canister housingat the proximal end;

FIG. 23B is a top plan view of an alternative S-ICD canister of thepresent invention having a duckbill-shaped canister housing with analternative proximal head configuration;

FIG. 24A is a top plan view of an alternative S-ICD canister of thepresent invention having a rectangular-shaped canister housing;

FIG. 24B is a top plan view of an alternative S-ICD canister of thepresent invention having a square-shaped canister housing with atriangular shaped electrode;

FIG. 24C is a top plan view of an alternative S-ICD canister of thepresent invention having a square-shaped canister housing with a squareshaped electrode;

FIG. 25A is a top plan view of an alternative S-ICD canister of thepresent invention having a tongue depressor-shaped canister housing;

FIG. 25B is a top plan view of an alternative S-ICD canister of thepresent invention having a modified tongue depressor-shaped canisterhousing;

FIG. 26A is a top plan view of an alternative S-ICD canister of thepresent invention having a multi-segment canister housing;

FIG. 26B is a front elevational view of the S-ICD canister of FIG. 26Adepicting the curved proximal segment and the planar distal segment ofthe multi-segment canister housing; and

FIG. 26C is a front elevational view of the S-ICD canister of FIG. 26Adepicting the curved proximal segment and the curved distal segment ofthe multi-segment canister housing.

DETAILED DESCRIPTION

Turning now to FIG. 1, the S-ICD of the present invention isillustrated. The S-ICD consists of an electrically active canister 11and a subcutaneous electrode 13 attached to the canister. The canisterhas an electrically active surface 15 that is electrically insulatedfrom the electrode connector block 17 and the canister housing 16 viainsulating area 14. The canister can be similar to numerous electricallyactive canisters commercially available in that the canister willcontain a battery supply, capacitor and operational circuitry.Alternatively, the canister can be thin and elongated to conform to theintercostal space. The circuitry will be able to monitor cardiac rhythmsfor tachycardia and fibrillation, and if detected, will initiatecharging the capacitor and then delivering cardioversion/defibrillationenergy through the active surface of the housing and to the subcutaneouselectrode. Examples of such circuitry are described in U.S. Pat. Nos.4,693,253 and 5,105,810, the entire disclosures of which are hereinincorporated by reference. The canister circuitry can providecardioversion/defibrillation energy in different types of waveforms. Inone embodiment, a 100 uF biphasic waveform is used of approximately10-20 ms total duration and with the initial phase containingapproximately ⅔ of the energy, however, any type of waveform can beutilized such as monophasic, biphasic, multiphasic or alternativewaveforms as is known in the art.

In addition to providing cardioversion/defibrillation energy, thecircuitry can also provide transthoracic cardiac pacing energy. Theoptional circuitry will be able to monitor the heart for bradycardiaand/or tachycardia rhythms. Once a bradycardia or tachycardia rhythm isdetected, the circuitry can then deliver appropriate pacing energy atappropriate intervals through the active surface and the subcutaneouselectrode. Pacing stimuli can be biphasic in one embodiment and similarin pulse amplitude to that used for conventional transthoracic pacing.

This same circuitry can also be used to deliver low amplitude shocks onthe T-wave for induction of ventricular fibrillation for testing S-ICDperformance in treating V-Fib as is described in U.S. Pat. No.5,129,392, the entire disclosure of which is hereby incorporated byreference. Also the circuitry can be provided with rapid induction ofventricular fibrillation or ventricular tachycardia using rapidventricular pacing. Another optional way for inducing ventricularfibrillation would be to provide a continuous low voltage, i.e., about 3volts, across the heart during the entire cardiac cycle.

Another optional aspect of the present invention is that the operationalcircuitry can detect the presence of atrial fibrillation as described inOlson, W. et al. “Onset And Stability For Ventricular TachyarrhythmiaDetection in an Implantable Cardioverter and Defibrillator,” Computersin Cardiology (1986) pp. 167-170. Detection can be provided via R-RCycle length instability detection algorithms. Once atrial fibrillationhas been detected, the operational circuitry will then provide QRSsynchronized atrial defibrillation/cardioversion using the same shockenergy and waveshape characteristics used for ventriculardefibrillation/cardioversion.

The sensing circuitry will utilize the electronic signals generated fromthe heart and will primarily detect QRS waves. In one embodiment, thecircuitry will be programmed to detect only ventricular tachycardias orfibrillations. The detection circuitry will utilize in its most directform, a rate detection algorithm that triggers charging of the capacitoronce the ventricular rate exceeds some predetermined level for a fixedperiod of time: for example, if the ventricular rate exceeds 240 bpm onaverage for more than 4 seconds. Once the capacitor is charged, aconfirmatory rhythm check would ensure that the rate persists for atleast another 1 second before discharge. Similarly, terminationalgorithms could be instituted that ensure that a rhythm less than 240bpm persisting for at least 4 seconds before the capacitor charge isdrained to an internal resistor. Detection, confirmation and terminationalgorithms as are described above and in the art can be modulated toincrease sensitivity and specificity by examining QRS beat-to-beatuniformity, QRS signal frequency content, R-R interval stability data,and signal amplitude characteristics all or part of which can be used toincrease or decrease both sensitivity and specificity of S-ICDarrhythmia detection function.

In addition to use of the sense circuitry for detection of V-Fib orV-Tach by examining the QRS waves, the sense circuitry can check for thepresence or the absence of respiration. The respiration rate can bedetected by monitoring the impedance across the thorax usingsubthreshold currents delivered across the active can and the highvoltage subcutaneous lead electrode and monitoring the frequency inundulation in the waveform that results from the undulations oftransthoracic impedance during the respiratory cycle. If there is noundulation, then the patient is not respiring and this lack ofrespiration can be used to confirm the QRS findings of cardiac arrest.The same technique can be used to provide information about therespiratory rate or estimate cardiac output as described in U.S. Pat.Nos. 6,095,987; 5,423,326; and 4,450,527, the entire disclosures ofwhich are incorporated herein by reference.

The canister of the present invention can be made out of titanium alloyor other presently preferred electrically active canister designs.However, it is contemplated that a malleable canister that can conformto the curvature of the patient's chest will be preferred. In this waythe patient can have a comfortable canister that conforms to the shapeof the patient's rib cage. Examples of conforming canisters are providedin U.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. Therefore, the canister can be made out ofnumerous materials such as medical grade plastics, metals, and alloys.In the preferred embodiment, the canister is smaller than 60 cc volumehaving a weight of less than 100 gms for long term wearability,especially in children. The canister and the lead of the S-ICD can alsouse fractal or wrinkled surfaces to increase surface area to improvedefibrillation capability. Because of the primary prevention role of thetherapy and the likely need to reach energies over 40 Joules, a featureof one embodiment is that the charge time for the therapy, isintentionally left relatively long to allow capacitor charging withinthe limitations of device size. Examples of small ICD housings aredisclosed in U.S. Pat. Nos. 5,597,956 and 5,405,363, the entiredisclosures of which are herein incorporated by reference.

Different subcutaneous electrodes 13 of the present invention areillustrated in FIGS. 1-3. Turning to FIG. 1, the lead 21 for thesubcutaneous electrode is preferably composed of silicone orpolyurethane insulation. The electrode is connected to the canister atits proximal end via connection port 19 which is located on anelectrically insulated area 17 of the canister. The electrodeillustrated is a composite electrode with three different electrodesattached to the lead. In the embodiment illustrated, an optional anchorsegment 52 is attached at the most distal end of the subcutaneouselectrode for anchoring the electrode into soft tissue such that theelectrode does not dislodge after implantation.

The most distal electrode on the composite subcutaneous electrode is acoil electrode 27 that is used for delivering the high voltagecardioversion/defibrillation energy across the heart. The coilcardioversion/defibrillation electrode is about 5-10 cm in length.Proximal to the coil electrode are two sense electrodes, a first senseelectrode 25 is located proximally to the coil electrode and a secondsense electrode 23 is located proximally to the first sense electrode.The sense electrodes are spaced far enough apart to be able to have goodQRS detection. This spacing can range from 1 to 10 cm with 4 cm beingpresently preferred. The electrodes may or may not be circumferentialwith the preferred embodiment. Having the electrodes non-circumferentialand positioned outward, toward the skin surface, is a means to minimizemuscle artifact and enhance QRS signal quality. The sensing electrodesare electrically isolated from the cardioversion/defibrillationelectrode via insulating areas 29. Similar types ofcardioversion/defibrillation electrodes are currently commerciallyavailable in a transvenous configuration. For example, U.S. Pat. No.5,534,022, the entire disclosure of which is herein incorporated byreference, disclosures a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement are contemplated within the scope ofthe invention. One such modification is illustrated in FIG. 2 where thetwo sensing electrodes 25 and 23 are non-circumferential sensingelectrodes and one is located at the distal end, the other is locatedproximal thereto with the coil electrode located in between the twosensing electrodes. In this embodiment the sense electrodes are spacedabout 6 to about 12 cm apart depending on the length of the coilelectrode used. FIG. 3 illustrates yet a further embodiment where thetwo sensing electrodes are located at the distal end to the compositeelectrode with the coil electrode located proximally thereto. Otherpossibilities exist and are contemplated within the present invention.For example, having only one sensing electrode, either proximal ordistal to the coil cardioversion/defibrillation electrode, with the coilserving as both a sensing electrode and a cardioversion/defibrillationelectrode.

It is also contemplated within the scope of the invention that thesensing of QRS waves (and transthoracic impedance) can be carried outvia sense electrodes on the canister housing or in combination with thecardioversion/defibrillation coil electrode and/or the subcutaneous leadsensing electrode(s). In this way, sensing could be performed via theone coil electrode located on the subcutaneous electrode and the activesurface on the canister housing. Another possibility would be to haveonly one sense electrode located on the subcutaneous electrode and thesensing would be performed by that one electrode and either the coilelectrode on the subcutaneous electrode or by the active surface of thecanister. The use of sensing electrodes on the canister would eliminatethe need for sensing electrodes on the subcutaneous electrode. It isalso contemplated that the subcutaneous electrode would be provided withat least one sense electrode, the canister with at least one senseelectrode, and if multiple sense electrodes are used on either thesubcutaneous electrode and/or the canister, that the best QRS wavedetection combination will be identified when the S-ICD is implanted andthis combination can be selected, activating the best sensingarrangement from all the existing sensing possibilities. Turning againto FIG. 2, two sensing electrodes 26 and 28 are located on theelectrically active surface 15 with electrical insulator rings 30 placedbetween the sense electrodes and the active surface. These canistersense electrodes could be switched off and electrically insulated duringand shortly after defibrillation/cardioversion shock delivery. Thecanister sense electrodes may also be placed on the electricallyinactive surface of the canister. In the embodiment of FIG. 2, there areactually four sensing electrodes, two on the subcutaneous lead and twoon the canister. In the preferred embodiment, the ability to changewhich electrodes are used for sensing would be a programmable feature ofthe S-ICD to adapt to changes in the patient physiology and size (in thecase of children) over time. The programming could be done via the useof physical switches on the canister, or as presently preferred, via theuse of a programming wand or via a wireless connection to program thecircuitry within the canister.

The canister could be employed as either a cathode or an anode of theS-ICD cardioversion/defibrillation system. If the canister is thecathode, then the subcutaneous coil electrode would be the anode.Likewise, if the canister is the anode, then the subcutaneous electrodewould be the cathode.

The active canister housing will provide energy and voltage intermediateto that available with ICDs and most AEDs. The typical maximum voltagenecessary for ICDs using most biphasic waveforms is approximately 750Volts with an associated maximum energy of approximately 40 Joules. Thetypical maximum voltage necessary for AEDs is approximately 2000-5000Volts with an associated maximum energy of approximately 200-360 Joulesdepending upon the model and waveform used. The S-ICD and the US-ICD ofthe present invention uses maximum voltages in the range of about 50 toabout 3500 Volts and is associated with energies of about 0.5 to about350 Joules. The capacitance of the devices can range from about 25 toabout 200 micro farads.

In another embodiment, the S-ICD and US-ICD devices provide energy witha pulse width of approximately one millisecond to approximately 40milliseconds. The devices can provide pacing current of approximatelyone milliamp to approximately 250 milliamps.

The sense circuitry contained within the canister is highly sensitiveand specific for the presence or absence of life threatening ventriculararrhythmias. Features of the detection algorithm are programmable andthe algorithm is focused on the detection of V-FIB and high rate V-TACH(>240 bpm). Although the S-ICD of the present invention may rarely beused for an actual life-threatening event, the simplicity of design andimplementation allows it to be employed in large populations of patientsat modest risk with modest cost by non-cardiac electrophysiologists.Consequently, the S-ICD of the present invention focuses mostly on thedetection and therapy of the most malignant rhythm disorders. As part ofthe detection algorithm's applicability to children, the upper raterange is programmable upward for use in children, known to have rapidsupraventricular tachycardias and more rapid ventricular fibrillation.Energy levels also are programmable downward in order to allow treatmentof neonates and infants.

Turning now to FIG. 4, the optimal subcutaneous placement of the S-ICDof the present invention is illustrated. As would be evidence to aperson skilled in the art, the actual location of the S-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the Figures only for help in understandingwhere the canister and coil electrode are three dimensionally located inthe left mid-clavicular line approximately at the level of theinframammary crease at approximately the 5th rib. The lead 21 of thesubcutaneous electrode traverses in a subcutaneous path around thethorax terminating with its distal electrode end at the posterioraxillary line ideally just lateral to the left scapula. This way thecanister and subcutaneous cardioversion/defibrillation electrode providea reasonably good pathway for current delivery to the majority of theventricular myocardium.

FIG. 5 illustrates a different placement of the present invention. TheS-ICD canister with the active housing is located in the left posterioraxillary line approximately lateral to the tip of the inferior portionof the scapula. This location is especially useful in children. The lead21 of the subcutaneous electrode traverses in a subcutaneous path aroundthe thorax terminating with its distal electrode end at the anteriorprecordial region, ideally in the inframammary crease. FIG. 6illustrates the embodiment of FIG. 1 subcutaneously implanted in thethorax with the proximal sense electrodes 23 and 25 located atapproximately the left axillary line with thecardioversion/defibrillation electrode just lateral to the tip of theinferior portion of the scapula.

FIG. 7 schematically illustrates the method for implanting the S-ICD ofthe present invention. An incision 31 is made in the left anterioraxillary line approximately at the level of the cardiac apex. Thisincision location is distinct from that chosen for S-ICD placement andis selected specifically to allow both canister location more mediallyin the left inframammary crease and lead positioning more posteriorlyvia the introducer set (described below) around to the left posterioraxillary line lateral to the left scapula. That said, the incision canbe anywhere on the thorax deemed reasonably by the implanting physicianalthough in the preferred embodiment, the S-ICD of the present inventionwill be applied in this region. A subcutaneous pathway 33 is thencreated medially to the inframammary crease for the canister andposteriorly to the left posterior axillary line lateral to the leftscapula for the lead.

The S-ICD canister 11 is then placed subcutaneously at the location ofthe incision or medially at the subcutaneous region at the leftinframammary crease. The subcutaneous electrode 13 is placed with aspecially designed curved introducer set 40 (see FIG. 8). The introducerset comprises a curved trocar 42 and a stiff curved peel away sheath 44.The peel away sheath is curved to allow for placement around the ribcage of the patient in the subcutaneous space created by the trocar. Thesheath has to be stiff enough to allow for the placement of theelectrodes without the sheath collapsing or bending. Preferably thesheath is made out of a biocompatible plastic material and is perforatedalong its axial length to allow for it to split apart into two sections.The trocar has a proximal handle 41 and a curved shaft 43. The distalend 45 of the trocar is tapered to allow for dissection of asubcutaneous path 33 in the patient. Preferably, the trocar iscannulated having a central Lumen 46 and terminating in an opening 48 atthe distal end. Local anesthetic such as lidocaine can be delivered, ifnecessary, through the lumen or through a curved and elongated needledesigned to anesthetize the path to be used for trocar insertion shouldgeneral anesthesia not be employed. The curved peel away sheath 44 has aproximal pull tab 49 for breaking the sheath into two halves along itsaxial shaft 47. The sheath is placed over a guidewire inserted throughthe trocar after the subcutaneous path has been created. Thesubcutaneous pathway is then developed until it terminatessubcutaneously at a location that, if a straight line were drawn fromthe canister location to the path termination point the line wouldintersect a substantial portion of the left ventricular mass of thepatient. The guidewire is then removed leaving the peel away sheath. Thesubcutaneous lead system is then inserted through the sheath until it isin the proper location. Once the subcutaneous lead system is in theproper location, the sheath is split in half using the pull tab 49 andremoved. If more than one subcutaneous electrode is being used, a newcurved peel away sheath can be used for each subcutaneous electrode.

The S-ICD will have prophylactic use in adults where chronictransvenous/epicardial ICD lead systems pose excessive risk or havealready resulted in difficulty, such as sepsis or lead fractures. It isalso contemplated that a major use of the S-ICD system of the presentinvention will be for prophylactic use in children who are at risk forhaving fatal arrhythmias, where chronic transvenous lead systems posesignificant management problems. Additionally, with the use of standardtransvenous ICDs in children, problems develop during patient growth inthat the lead system does not accommodate the growth. FIG. 9 illustratesthe placement of the S-ICD subcutaneous lead system such that he problemthat growth presents to the lead system is overcome. The distal end ofthe subcutaneous electrode is placed in the same location as describedabove providing a good location for the coilcardioversion/defibrillation electrode 27 and the sensing electrodes 23and 25. The insulated lead 21, however, is no longer placed in a tautconfiguration. Instead, the lead is serpiginously placed with aspecially designed introducer trocar and sheath such that it hasnumerous waves or bends. As the child grows, the waves or bends willstraighten out lengthening the lead system while maintaining properelectrode placement. Although it is expected that fibrous scarringespecially around the defibrillation coil will help anchor it intoposition to maintain its posterior position during growth, a lead systemwith a distal tine or screw electrode anchoring system 52 can also beincorporated into the distal tip of the lead to facilitate leadstability (see FIG. 1). Other anchoring systems can also be used such ashooks, sutures, or the like.

FIGS. 10 and 11 illustrate another embodiment of the present S-ICDinvention. In this embodiment there are two subcutaneous electrodes 13and 13′ of opposite polarity to the canister. The additionalsubcutaneous electrode 13′ is essentially identical to the previouslydescribed electrode. In this embodiment the cardioversion/defibrillationenergy is delivered between the active surface of the canister and thetwo coil electrodes 27 and 27′. Additionally, provided in the canisteris means for selecting the optimum sensing arrangement between the foursense electrodes 23, 23′, 25, and 25′. The two electrodes aresubcutaneously placed on the same side of the heart. As illustrated inFIG. 6, one subcutaneous electrode 13 is placed inferiorly and the otherelectrode 13′ is placed superiorly. It is also contemplated with thisdual subcutaneous electrode system that the canister and onesubcutaneous electrode are the same polarity and the other subcutaneouselectrode is the opposite polarity.

Turning now to FIGS. 12 and 13, further embodiments are illustratedwhere the canister 11 of the S-ICD of the present invention is shaped tobe particularly useful in placing subcutaneously adjacent and parallelto a rib of a patient. The canister is long, thin, and curved to conformto the shape of the patient's rib. In the embodiment illustrated in FIG.12, the canister has a diameter ranging from about 0.5 cm to about 2 cmwithout 1 cm being presently preferred. Alternatively, instead of havinga circular cross sectional area, the canister could have a rectangularor square cross sectional area as illustrated in FIG. 13 without fallingoutside of the scope of the present invention. The length of thecanister can vary depending on the size of the patient's thorax. In anembodiment, the canister is about 5 cm to about 40 cm long. The canisteris curved to conform to the curvature of the ribs of the thorax. Theradius of the curvature will vary depending on the size of the patient,with smaller radiuses for smaller patients and larger radiuses forlarger patients. The radius of the curvature can range from about 5 cmto about 35 cm depending on the size of the patient. Additionally, theradius of the curvature need not be uniform throughout the canister suchthat it can be shaped closer to the shape of the ribs. The canister hasan active surface, 15 that is located on the interior (concave) portionof the curvature and an inactive surface 16 that is located on theexterior (convex) portion of the curvature. The leads of theseembodiments, which are not illustrated except for the attachment port 19and the proximal end of the lead 21, can be any of the leads previouslydescribed above, with the lead illustrated in FIG. 1 being presentlypreferred.

The circuitry of this canister is similar to the circuitry describedabove. Additionally, the canister can optionally have at least one senseelectrode located on either the active surface of the inactive surfaceand the circuitry within the canister can be programmable as describedabove to allow for the selection of the best sense electrodes. It ispresently preferred that the canister have two sense electrodes 26 and28 located on the inactive surface of the canisters as illustrated,where the electrodes are spaced from about 1 to about 10 cm apart with aspacing of about 3 cm being presently preferred. However, the senseelectrodes can be located on the active surface as described above.

It is envisioned that the embodiment of FIG. 12 will be subcutaneouslyimplanted adjacent and parallel to the left anterior 5th rib, eitherbetween the 4th and 5th ribs or between the 5th and 6th ribs. Howeverother locations can be used.

Another component of the S-ICD of the present invention is a cutaneoustest electrode system designed to simulate the subcutaneous high voltageshock electrode system as well as the QRS cardiac rhythm detectionsystem. This test electrode system is comprised of a cutaneous patchelectrode of similar surface area and impedance to that of the S-ICDcanister itself together with a cutaneous strip electrode comprising adefibrillation strip as well as two button electrodes for sensing of theQRS. Several cutaneous strip electrodes are available to allow fortesting various bipole spacings to optimize signal detection comparableto the implantable system.

FIGS. 14 to 18 depict particular US-ICD embodiments of the presentinvention. The various sensing, shocking and pacing circuitry, describedin detail above with respect to the S-ICD embodiments, may additionallybe incorporated into the following US-ICD embodiments. Furthermore,particular aspects of any individual S-ICD embodiment discussed abovemay be incorporated, in whole or in part, into the US-ICD embodimentsdepicted in the following Figures.

Turning now to FIG. 14, the US-ICD of the present invention isillustrated. The US-ICD consists of a curved housing 1211 with a firstand second end. The first end 1413 is thicker than the second end 1215.This thicker area houses a battery supply, capacitor and operationalcircuitry for the US-ICD. The circuitry will be able to monitor cardiacrhythms for tachycardia and fibrillation, and if detected, will initiatecharging the capacitor and then delivering cardioversion/defibrillationenergy through the two cardioversion/defibrillating electrodes 1417 and1219 located on the outer surface of the two ends of the housing. Thecircuitry can provide cardioversion/defibrillation energy in differenttypes of waveforms. In one embodiment, a 100 uF biphasic waveform isused of approximately 10-20 ms total duration and with the initial phasecontaining approximately ⅔ of the energy, however, any type of waveformcan be utilized such as monophasic, biphasic, multiphasic or alternativewaveforms as is known in the art.

The housing of the present invention can be made out of titanium alloyor other presently preferred ICD designs. It is contemplated that thehousing is also made out of biocompatible plastic materials thatelectronically insulate the electrodes from each other. However, it iscontemplated that a malleable canister that can conform to the curvatureof the patient's chest will be preferred. In this way the patient canhave a comfortable canister that conforms to the unique shape of thepatient's rib cage. Examples of conforming ICD housings are provided inU.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. In the preferred embodiment, the housing iscurved in the shape of a 5th rib of a person. Because there are manydifferent sizes of people, the housing will come in differentincremental sizes to allow a good match between the size of the rib cageand the size of the US-ICD. The length of the US-ICD will range fromabout 15 to about 50 cm. Because of the primary preventative role of thetherapy and the need to reach energies over 40 Joules, a feature of thepreferred embodiment is that the charge time for the therapy,intentionally be relatively long to allow capacitor charging within thelimitations of device size.

The thick end of the housing is currently needed to allow for theplacement of the battery supply, operational circuitry, and capacitors.It is contemplated that the thick end will be about 0.5 cm to about 2 cmwide with about 1 cm being presently preferred. As microtechnologyadvances, the thickness of the housing will become smaller.

The two cardioversion/defibrillation electrodes on the housing are usedfor delivering the high voltage cardioversion/defibrillation energyacross the heart. In the preferred embodiment, thecardioversion/defibrillation electrodes are coil electrodes, however,other cardioversion/defibrillation electrodes could be used such ashaving electrically isolated active surfaces or platinum alloyelectrodes. The coil cardioversion/defibrillation electrodes are about5-10 cm in length. Located on the housing between the twocardioversion/defibrillation electrodes are two sense electrodes 1425and 1427. The sense electrodes are spaced far enough apart to be able tohave good QRS detection. This spacing can range from 1 to 10 cm with 4cm being presently preferred. The electrodes may or may not becircumferential with the preferred embodiment. Having the electrodesnon-circumferential and positioned outward, toward the skin surface, isa means to minimize muscle artifact and enhance QRS signal quality. Thesensing electrodes are electrically isolated from thecardioversion/defibrillation electrode via insulating areas 1423.Analogous types of cardioversion/defibrillation electrodes are currentlycommercially available in a transvenous configuration. For example, U.S.Pat. No. 5,534,022, the entire disclosure of which is hereinincorporated by reference, discloses a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement are contemplated within the scope ofthe invention. One such modification is to have the sense electrodes atthe two ends of the housing and have the cardioversion/defibrillationelectrodes located in between the sense electrodes. Another modificationis to have three or more sense electrodes spaced throughout the housingand allow for the selection of the two best sensing electrodes. If threeor more sensing electrodes are used, then the ability to change whichelectrodes are used for sensing would be a programmable feature of theUS-ICD to adapt to changes in the patient physiology and size over time.The programming could be done via the use of physical switches on thecanister, or as presently preferred, via the use of a programming wandor via a wireless connection to program the circuitry within thecanister.

Turning now to FIG. 15, the optimal subcutaneous placement of the US-ICDof the present invention is illustrated. As would be evident to a personskilled in the art, the actual location of the US-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the Figures only for help in understandingwhere the device and its various electrodes are three dimensionallylocated in the thorax of the patient. The US-ICD is located between theleft mid-clavicular line approximately at the level of the inframammarycrease at approximately the 5th rib and the posterior axillary line,ideally just lateral to the left scapula. This way the US-ICD provides areasonably good pathway for current delivery to the majority of theventricular myocardium.

FIG. 16 schematically illustrates the method for implanting the US-ICDof the present invention. An incision 1631 is made in the left anterioraxillary line approximately at the level of the cardiac apex. Asubcutaneous pathway is then created that extends posteriorly to allowplacement of the US-ICD. The incision can be anywhere on the thoraxdeemed reasonable by the implanting physician although in the preferredembodiment, the US-ICD of the present invention will be applied in thisregion. The subcutaneous pathway is created medially to the inframammarycrease and extends posteriorly to the left posterior axillary line. Thepathway is developed with a specially designed curved introducer 1742(see FIG. 17). The trocar has a proximal handle 1641 and a curved shaft1643. The distal end 1745 of the trocar is tapered to allow fordissection of a subcutaneous path in the patient. Preferably, the trocaris cannulated having a central lumen 1746 and terminating in an opening1748 at the distal end. Local anesthetic such as lidocaine can bedelivered, if necessary, through the lumen or through a curved andelongated needle designed to anesthetize the path to be used for trocarinsertion should general anesthesia not be employed. Once thesubcutaneous pathway is developed, the US-ICD is implanted in thesubcutaneous space, the skin incision is closed using standardtechniques.

As described previously, the US-ICDs of the present invention vary inlength and curvature. The US-ICDs are provided in incremental sizes forsubcutaneous implantation in different sized patients. Turning now toFIG. 18, a different embodiment is schematically illustrated in explodedview which provides different sized US-ICDs that are easier tomanufacture. The different sized US-ICDs will all have the same sizedand shaped thick end 1413. The thick end is hollow inside allowing forthe insertion of a core operational member 1853. The core membercomprises a housing 1857 which contains the battery supply, capacitorand operational circuitry for the US-ICD. The proximal end of the coremember has a plurality of electronic plug connectors. Plug connectors1861 and 1863 are electronically connected to the sense electrodes viapressure fit connectors (not illustrated) inside the thick end which arestandard in the art. Plug connectors 1865 and 1867 are alsoelectronically connected to the cardioverter/defibrillator electrodesvia pressure fit connectors inside the thick end. The distal end of thecore member comprises an end cap 1855, and a ribbed fitting 1859 whichcreates a water-tight seal when the core member is inserted into opening1851 of the thick end of the US-ICD.

The S-ICD and US-ICD, in alternative embodiments, have the ability todetect and treat atrial rhythm disorders, including atrial fibrillation.The S-ICD and US-ICD have two or more electrodes that provide afar-field view of cardiac electrical activity that includes the abilityto record the P-wave of the electrocardiogram as well as the QRS. Onecan detect the onset and offset of atrial fibrillation by referencing tothe P-wave recorded during normal sinus rhythm and monitoring for itschange in rate, morphology, amplitude and frequency content. Forexample, a well-defined P-wave that abruptly disappeared and wasreplaced by a low-amplitude, variable morphology signal would be astrong indication of the absence of sinus rhythm and the onset of atrialfibrillation. In an alternative embodiment of a detection algorithm, theventricular detection rate could be monitored for stability of the R-Rcoupling interval. In the examination of the R-R interval sequence,atrial fibrillation can be recognized by providing a near constantirregularly irregular coupling interval on a beat-by-beat basis. An R-Rinterval plot during AF appears “cloudlike” in appearance when severalhundred or thousands of R-R intervals are plotted over time whencompared to sinus rhythm or other supraventricular arrhythmias.Moreover, a distinguishing feature compared to other rhythms that areirregularly irregular, is that the QRS morphology is similar on abeat-by-beat basis despite the irregularity in the R-R couplinginterval. This is a distinguishing feature of atrial fibrillationcompared to ventricular fibrillation where the QRS morphology varies ona beat-by-beat basis. In yet another embodiment, atrial fibrillation maybe detected by seeking to compare the timing and amplitude relationshipof the detected P-wave of the electrocardiogram to the detected QRS(R-wave) of the electrocardiogram. Normal sinus rhythm has a fixedrelationship that can be placed into a template matching algorithm thatcan be used as a reference point should the relationship change.

In other aspects of the atrial fibrillation detection process, one mayinclude alternative electrodes that may be brought to bear in the S-ICDor US-ICD systems either by placing them in the detection algorithmcircuitry through a programming maneuver or by manually adding suchadditional electrode systems to the S-ICD or US-ICD at the time ofimplant or at the time of follow-up evaluation. One may also useelectrodes for the detection of atrial fibrillation that may or may notalso be used for the detection of ventricular arrhythmias given thedifferent anatomic locations of the atria and ventricles with respect tothe S-ICD or US-ICD housing and surgical implant sites.

Once atrial fibrillation is detected, the arrhythmia can be treated bydelivery of a synchronized shock using energy levels up to the maximumoutput of the device therapy for terminating atrial fibrillation or forother supraventricular arrhythmias. The S-ICD or US-ICD electrode systemcan be used to treat both atrial and ventricular arrhythmias not onlywith shock therapy but also with pacing therapy. In a further embodimentof the treatment of atrial fibrillation or other atrial arrhythmias, onemay be able to use different electrode systems than what is used totreat ventricular arrhythmias. Another embodiment would be to allow fordifferent types of therapies (amplitude, waveform, capacitance, etc.)for atrial arrhythmias compared to ventricular arrhythmias.

The core member of the different sized and shaped US-ICD will all be thesame size and shape. That way, during an implantation procedure,multiple sized US-ICDs can be available for implantation, each onewithout a core member. Once the implantation procedure is beingperformed, then the correct sized US-ICD can be selected and the coremember can be inserted into the US-ICD and then programmed as describedabove. Another advantage of this configuration is when the batterywithin the core member needs replacing it can be done without removingthe entire US-ICD.

FIGS. 19-26 refer generally to alternative S-ICD/US-ICD canisterembodiments. Although the following canister designs, various materialconstructions, dimensions and curvatures discussed in detail below maybe incorporated into either S-ICD or US-ICD canister embodiments,hereinafter, these attributes will be discussed solely with respect toS-ICDs.

The canisters illustrated in these Figures possess a configuration thatmay 1) aid in the initial canister implantation; 2) restrict canisterdisplacement once properly positioned; 3) create a consistently focusedarray of energy delivered toward the recipient's heart with lessdisbursement to other areas of the thorax; 4) allow for good signalreception from the heart by an S-ICD system; or 5) provide significantcomfort and long-term wearability in a broad spectrum of patients withdiffering thoracic sizes and shapes. More particularly, FIGS. 19-26detail various material constructions, dimensions and curvatures thatare incorporated within the numerous S-ICD canister designs detailed inFIGS. 19-26C.

Referring now to the particular embodiments, FIG. 19 depicts an S-ICDcanister 190 of an embodiment of the present invention. The shell of theS-ICD canister 190 comprises a hermetically sealed housing 192 thatencases the electronics for the S-ICD canister 190. As with thepreviously described S-ICD devices, the electronics of the presentembodiment include, at a minimum, a battery supply, a capacitor andoperational circuitry. FIG. 19 further depicts a lead electrode 191coupled to the shell of the canister through a lead 193. A dorsal fin197 may be disposed on the lead electrode 191 to facilitate thepositioning of the lead electrode.

The S-ICD devices of the present invention provide an energy (electricfield strength (V/cm), current density (A/cm2), voltage gradient (V/cm)or other measured unit of energy) to a patient's heart. S-ICD devices ofthe present invention will generally use voltages in the range of 350 Vto 3500 V, requiring energies of approximately 0.5 J to 350 J. Theseenergy requirements will vary, however, depending upon the form oftreatment, the proximity of the canister from the patient's heart, therelative relationship of the S-ICD canister's electrode to the leadelectrode, the nature of the patient's underlying heart disease, thespecific cardiac disorder being treated, and the ability to overcomediversion of the S-ICD electrical output into other thoracic tissues.

Ideally, the emitted energy from the S-ICD device will be directed intothe patient's anterior mediastinum, through the majority of the heart,and out to the coupled lead electrode positioned in the posterior,posterolateral and/or lateral thoracic locations. Furthermore, it isdesirable that the S-ICD canister 190 be capable of delivering thisdirected energy, as a general rule, at an adequate effective fieldstrength of about 3-5 V/cm to approximately 90 percent of a patient'sventricular myocardium using a biphasic waveform. This deliveredeffective field strength should be adequate for defibrillation of thepatient's heart—an intended application of an embodiment of the presentinvention.

Increased energy requirements necessitate larger, or alternatively,additional batteries and capacitors. The latter of these two options isoften more desirable in order to reduce the overall depth of theresulting S-ICD canister 190. Increasing the number of batteries andcapacitors, however, will increase the length and possibly the depth ofthe S-ICD canister 190. Therefore, numerous S-ICD devices of varyingdepth, widths and lengths are manufactured to accommodate the particularenergy needs of a variety of patient recipients. For example, anoverweight adult male may require a larger and bulkier S-ICD canister190 than a young child. In particular, the young child is generallysmaller, has a relatively lower resistance to current flow, and containsless current diverting body mass than the overweight adult male. As aresult, the energy required to deliver an effective therapy to the youngchild's heart may be considerably less than for the overweight adultmale, and therefore, the young child may utilize a smaller and morecompact S-ICD canister 190. In addition, one may find that individuals,despite equivalent body size, may have different therapy requirementsbecause of differences in their underlying heart disease. This may allowsome patients to receive a smaller canister compared to another patientof equal body size but with a different type of heart disease.

The spatial requirements of a resulting S-ICD canister 190 areadditionally dependent upon the type of operational circuitry usedwithin the device. The S-ICD canister 190 may be programmed to monitorcardiac rhythms for tachycardia and fibrillation, and if detected, willinitiate charging the capacitor(s) to deliver the appropriatecardioversion/defibrillation energy. Examples of such circuitry aredescribed in U.S. Pat. Nos. 4,693,253 and 5,105,810, the entiredisclosures of which are incorporated herein by reference. The S-ICDcanister 190 may additionally be provided with operational circuitry fortransthoracic cardiac pacing. This optional circuitry monitors the heartfor bradycardia and/or tachycardia rhythms. In the event a bradycardiaor tachycardia rhythm is detected, the operational circuitry deliversthe appropriate pacing energy at the appropriate intervals to treat thedisorder.

In additional embodiments, the operational circuitry may be: 1)programmed to deliver low amplitude shocks on the T-wave for inductionof ventricular fibrillation for testing the S-ICD canister'sperformance; 2) programmed for rapid ventricular pacing to either inducea tachyarrhythmia or to terminate one; 3) programmed to detect thepresence of atrial fibrillation; and/or 4) programmed to detectventricular fibrillation or ventricular tachycardia by examining QRSwaves, all of which are described in detail above. Additionaloperational circuitry, being known in the art for sensing, shocking andpacing the heart, are additionally incorporated herein as being withinthe spirit and scope of the present invention.

The primary function of the canister housing 192 is to provide aprotective barrier between the electrical components held within itsconfines and the surrounding environment. The canister housing 192,therefore, must possess sufficient hardness to protect its contents.Materials possessing this hardness may include numerous suitablebiocompatible materials such as medical grade plastics, ceramics, metalsand alloys. Although the materials possessing such hardnesses aregenerally rigid, in particular embodiments, it is desirable to utilizematerials that are pliable or compliant. More specifically, it isdesirable that the canister housing 192 be capable of partially yieldingin its overall form without fracturing.

Compliant canister housings 192 often provide increased comfort whenimplanted in patient recipients. S-ICD canisters 190 formed from suchmaterials permit limited, but significant, deflection of the canisterhousing 192 with certain thoracic motions. Examples of permitteddeflections are ones that are applied to the canister housing 192 bysurrounding muscle tissue. The use of a compliant canister housing isparticularly beneficial in canister housing embodiments that extend overa significant portion of a patient's thorax. The compliant material inthese embodiments may comprise a portion of the canister housing, oralternatively, may comprise the canister housing in its entirety. Thecorrect material selection (or combination thereof), therefore, ishelpful in eliminating patient awareness of the device and in improvingthe long-term wearability of the implanted device.

Materials selected for the canister housing 192 should further becapable of being sterilized. Often commercial sterilization processesinvolve exposure to elevated temperatures, pressures or chemicaltreatments. It is important, therefore, that the materials used informing the canister housing be capable of withstanding such exposureswithout degrading or otherwise compromising their overall integrity.

Polymeric materials suitable for the canister housing 192 of the presentinvention include polyurethanes, polyamides, polyetheretherketones(PEEK), polyether block amides (PEBA), polytetrafluoroethylene (PTFE),silicones, and mixtures thereof. Ceramic materials suitable for thecanister housing 192 of the present invention include zirconium ceramicsand aluminum-based ceramics. Metallic materials suitable for thecanister housing 192 of the present invention include stainless steel,and titanium. Alloys suitable for the canister housing 192 of thepresent invention include stainless steel alloys and titanium alloyssuch as nickel titanium. In certain embodiments of the presentinvention, classes of materials may be combined in forming the canisterhousing 192. For example, a nonconductive polymeric coating, such asparylene, may be selectively applied over a titanium alloy canisterhousing 192 surface in order to allow only a specific surface area, suchas that at the undersurface of the duckbill distal end, to receivesignals and/or apply therapy.

In general, it is desirable to maintain the size of the S-ICD canisterhousing 192 under a total volume of approximately 50 cubic centimeters.In alternative embodiments of the present invention, it is desirable tomaintain the size of the S-ICD canister housing 192 under a total volumeof approximately 100 cubic centimeters. In yet alternative embodimentsof the present invention, it is desirable to maintain the size of theS-ICD canister housing 192 under a total volume of approximately 120cubic centimeters.

Moreover, it is additionally desirable to maintain the total weight ofthe S-ICD canister 190, as a whole (including the canister housing,operational circuitry, capacitors and batteries), under approximately 50grams. In alternative embodiments of the present invention, it isdesirable to maintain the total weight of the S-ICD canister 190 underapproximately 100 grams. In yet alternative embodiments of the presentinvention, it is desirable to maintain the total weight of the S-ICDcanister 190 under approximately 150 grams.

Maintaining the weight and size within the above identified parametersis primarily for patient comfort depending upon the shape of the device.The implantation of an S-ICD canister 190 is a long-term solution toheart dysfunction, and as such, will ideally remain in the patient untilthe device's batteries need replacement or an alternative therapyeventually leads to its removal. Accordingly, a considerable amount ofengineering is devoted to minimizing discomfort associated with theinstalled device.

Weight and size considerations are particularly important to youngerpatient recipients. Children possessing ICDs are more likely to becognitive of any additional weight or bulkiness associated with heavierand/or larger devices. The present invention overcomes these problems bydesigning an S-ICD canister 190 that takes into consideration theconcerns of these smaller sized patient recipients. For example, lightermaterials may be utilized to minimize discomfort associated with heaviermaterials. Furthermore, the S-ICD canister 190 (length, width and depth)in its entirety, or only a portion thereof, may be modified in order toaccommodate a variety of sized patient recipients. For example, theshape of the S-ICD canister housing 192 may also be manufactured in avariety of anatomical configurations to better insure comfort andperformance in younger children or smaller adults, throughout the lifeof their S-ICD canisters 190. In order to accommodate certain patients,a physician may place the canister 190 posteriorly with the leadelectrode positioned anteriorly with the patient's body, the reverse ofthe canister's 190 usual positioning. This canister 190 placement isparticularly useful when implanted in very small children. Such canister190 placement generally optimizes comfort for these smaller staturerecipients. Moreover, the shape of the canister 190 may be alteredspecifically to conform to a female's thorax, where breast tissue mayalter comfort and performance requirements.

Referring now to specific portions of the canister housing 192, FIG. 19depicts a canister housing 192 in accordance with one embodiment of thepresent invention having a top surface 194, a bottom surface 196 andsurrounding sides 198 connecting these two surfaces. The S-ICD canisterhousing 192 depicted in FIG. 19 further includes a distal end 200 and aproximal end 202. In particular canister housing embodiments, thecanister housing 192 may lack a proximal end and a distal end.

The top surface 194 of the canister housing 192 is generally smooth andvoid of appendages and apertures. The smooth top surface 194 enables theS-ICD canister 190 to advance effortlessly through the subcutaneoustissues during an implantation procedure. Smoothing the top surface 194reduces the coefficient of friction of the S-ICD canister 190. Suchmeasures reduce abrasion, and concurrently, also reduce inflammationassociated with the device's insertion and advancement. The benefits ofa reduction in surface friction also continue on long after implantationthrough a significant reduction in inflammation and soreness, lending toan overall heightened feeling of wearability and comfort.

In alternative embodiments, the top surface 194 of the canister housing192 may include one or more apertures, sensors, electrodes, appendages,or a combination thereof. Apertures on the top surface 194 of thecanister housing 192 are generally in the form of a connection port 203,or multiple connection ports, for coupling ancillary devices to thecanister itself. More specifically, the connection ports 203 couple theoperational circuitry housed within the canister to these ancillarydevices, as well as to a lead electrode 191. Connection ports 203 may bepositioned anywhere along the canister housing 192, however, inparticular embodiments, the connection ports 203 are located at thedistal end 200 or proximal end 202 of the canister housing 192. Theconnection ports 203 may additionally be positioned along the canisterhousing's sides 198 and bottom surface 196.

In yet another embodiment, connection ports 203 are located at both thedistal end 200 and the proximal end 202 of the canister housing 192.Positioning connection ports 203 at both the canister's distal end 200and the proximal end 202 may enhance the care provided by the S-ICDcanister 190. In particular, this canister arrangement allows theoperational circuitry in the S-ICD canister 190 to utilize multipleelectrodes and sensors to best regulate and treat the particularcondition experienced by the patient recipient. Examples of ancillarydevices suitable for attachment include a lead 193, such as a lead forsensing, shocking and pacing. Additional ancillary devices suitable forattachment to the S-ICD canister 190, being known in the art, (e.g.,heart failure monitoring sensors) are additionally incorporated as beingwithin the spirit and scope of the present invention.

The top surface 194 of the canister housing 192 may additionally includeparticular appendages. Appendages are especially useful in anchoring thecanister housing 192 in a fixed relative position, or alternatively, inadvancing the canister housing 192 within the patient recipient. Anexample of an appendage that may be incorporated into the top surface194 of the canister housing 192 is an extending fin. A fin-likeappendage may extend from the canister housing 192 in order to betterdirect the S-ICD canister 190 during the implantation procedure. In thiscapacity, the extended fin acts as a rudder preventing the advancingS-ICD canister 190 from deviating from its desired path. The extendedfin may additionally aid in preventing the S-ICD canister 190 fromdisplacing from its original position after implantation—particularly inthe direction perpendicular to the fin's length. Extending fins suitablefor the present invention may extend the entire length of the canisterhousing 192, or alternatively, a segment of the length. Additionally,extending fins may be disposed on the bottom surface 196 of the canisterhousing 192 in order to provide similar functions.

Appendages may also aid physicians in advancing the S-ICD canister 190to a desired location within the patient. Motility-enhancing appendagesenable the physician to push, pull or otherwise direct the S-ICDcanister 190 in a particular fashion throughout the patient's body.During the procedure, a physician generally attaches a medicalinstrument to the motility-enhancing appendage. This attachment step mayoccur either before or after the S-ICD canister 190 has been insertedwithin the patient. An example of one medical instrument capable ofattaching to the motility-enhancing appendage is a hemostat. Othersimilar medical instruments, known to those skilled in the art, may alsobe utilized in this attachment step. The physician then advances thehemostat in a desired direction to properly seat the S-ICD canister 190within the patient's body.

The surrounding sides 198 of the canister housing 192 are generallysmooth and substantially rounded between the top surface 194 and thebottom surface 196 of the canister housing 192. Smoothing the sidesurfaces 198 aids in the insertion of the S-ICD canister 190 during theimplantation procedure. More specifically, smoother side surfaces 198permit the S-ICD canister 190, as a whole, to slide easily through thesurrounding bodily tissue while minimizing abrasion. In addition,rounded, smooth transition surfaces allow the surrounding tissues tobetter conform to the presence of the device making the device morecomfortable to the patient during chronic implantation.

In contrast, sharp edge formations may have the tendency to ablate, orat a minimum, irritate the surrounding tissue during the implantationprocess. Subsequent tissue irritation may also occur long after theimplantation process. Minor fluctuations in the positioning of a sharpedged canister may cause an inflammatory response in the surroundingtissue. These minor fluctuations are often the result of simpleday-to-day movements. Movement of the arms, bending at the waist androtation of the torso are all daily activities that may causesurrounding bodily tissue to chafe against the installed canister.Smoothing these edges, however, would greatly reduce tissue abrasion,and thereby, reduce the soreness and discomfort associated with theimplanted S-ICD canister 190.

Referring now to FIG. 20, the bottom surface 196 of the S-ICD canister190 of FIG. 19 is shown. In particular, an electrode 204 possessing anelectrically conductive surface is depicted within the confines of, andhermetically sealed within, the S-ICD canister housing 192. Although anelectrode 204 is specifically illustrated, any sensor capable ofreceiving physiological information and/or emitting an energy may besimilarly situated on the canister housing 192. For example, a sensormay be located on the canister housing 192 that may monitor a patient'sblood glucose level, respiration, blood oxygen content, blood pressureand/or cardiac output.

Specifically with reference to FIG. 20, the exposed electrode 204 iselectrically coupled to the operational circuitry encased within thecanister housing 192. The electrode 204, therefore, performs many of thefunctions defined by the operational circuitry's programming. Morespecifically, the electrode 204 is the vehicle that actually receivesthe signals being monitored, and/or emits the energy required to pace,shock or otherwise stimulate the heart. Although only a single electrode204 is shown for illustrative purposes, certain S-ICD canisterembodiments 190 may be manufactured with multiple electrodes. For theseembodiments, the multiple electrodes are often task specific, whereineach electrode 204 performs a single function. In alternate embodiments,a single electrode 204 may perform both monitoring and shockingfunctions.

The electrodes 204 are generally positioned at the ends 200 and 202 ofthe canister housing 192. In the S-ICD canister 190 depicted in FIG. 20,the electrode 204 is placed at the distal end 200 of the canisterhousing 192. Although the electrode 204 is positioned in close proximityto the distal end 200, the side 198 of the canister housing 192 nearestthe distal end 200 should generally refrain from exposing any portion ofthe electrically conductive surface of the electrode 204. Additionally,although the electrode is generally planar, in particular embodiments,the electrode may possess a curved shape.

The size of the electrically conductive surface of an electrode 204, inone particular embodiment, is approximately 500 square millimeters inarea. In alternate embodiments, it is desirable to maintain the size ofthe electrically conductive surface between approximately 100 squaremillimeters and approximately 5000 square millimeters in area. As withthe size of the canister housing 192, the size of the electricallyconductive surface may vary to accommodate the particular patientrecipient. Furthermore, the shape and size of an electrode 204 may varyto accommodate the placement of the electrode 204 on the canisterhousing 192. The shape and size of an electrode may also be varied toadapt to specified diagnostic and therapeutic functions performed by thecanister 190. For example, the electrode's 204 size and shape may bealtered to minimize energy loss to surrounding bodily tissues, or forminimizing the diversion of current away from the heart.

One factor in minimizing current diversion is in maintaining an equalcurrent density distribution throughout an electrode's 204 conductivesurface. A controlling factor in an electrode's 204 current densitydistribution is the electrode's 204 overall shape. Certain electrode 204shapes draw current to particular areas on the electrode's 204conductive surface (e.g., sharp angles). As a result, these electrodes204 create an unequal current density distribution. Electrodes 204possessing sharp corners, for example, may have higher current densitiesin the regions defined by the sharp corner. This unequal current densitydistribution results in confined “hot spots”. The formation of hot spotsmay be desirable and intentional, such as when attempting to increasecurrent density adjacent to the sternum. On the other hand, hot spotsmay be undesirable as these high current density locations may scorch orsinge surrounding tissue during the electrode's 204 emission ofelectrical energy. Moreover, electrodes 204 possessing numerous hotspots on the electrode's 204 conductive surface consequently generateareas of low current density—or “cold spots”. This unequal distributionmay render the electrode 204, as a whole, highly ineffective.

Electrode 204 embodiments of the present invention, in contrast, aresubstantially rounded. In particular, regions of the electrode 204traditionally possessing sharp corners are rounded to prevent extremehot spots. Nevertheless, the distal most segment of the electrode 200 isslightly angulated in order to modestly concentrate current at the tip,and therefore, direct current more through the mediastinum and into thepatient's heart.

Another controlling factor in an electrode's 204 current densitydistribution is the electrode's 204 overall size. The relatively smallconductive surfaces of electrodes 204 of the present invention, asdiscussed above, minimize the likelihood of forming either hot or coldspots. Larger electrodes, in contrast, possess large surface areas thatmay be more prone to generate more regions of unequal currentdistribution.

As discussed above, electrodes 204 may vary in shape and size toaccommodate an assortment of canister housing 192 designs. Forillustrative purposes, FIG. 20 and FIGS. 23A-25A show various electrodeshapes disposed upon various canister housings 192. The canisterhousings 192 depicted in these Figures, however, are not limited to theelectrode shape specifically illustrated.

The electrode 204 depicted in FIG. 20 is “thumbnail” shaped. The distalend margin 206 of this shaped electrode 204 generally follows theoutline of the rounded distal end 200 of the canister housing 192. Asthe electrode 204 moves proximally along the length of the canisterhousing 192, the conductive surface terminates. In the thumbnailembodiment, the electrode's conductive surface is generally containedwithin the rounded portions of the distal end 200 of the canisterhousing 192. In alternate embodiments, the electrode's conductivesurface may extend proximally further within the canister housing 192.In yet another thumbnail shaped electrode embodiment, the margins of theelectrode's conductive surface refrain from following the exact roundedcontour of the canister housing 192.

A “spade” shaped electrode 236 is depicted in FIG. 23A. The distal endof the spade shaped electrode also generally follows the outline of therounded distal end 234 of the canister housing 220. As the spade shapedelectrode 236 moves proximally along the length of the canister housing220, the conductive surface terminates in a rounded proximal end.Similar to the thumbnail embodiment described above, the spade shapedelectrode's conductive surface is generally contained within the distalend 234 of the canister housing 220. In alternate embodiments, the spadeshape electrode's conductive surface may extend proximally furtherwithin the canister housing 220. In yet another spade shaped electrode234 embodiment, the margins of the spade shaped electrode's conductivesurface refrain from following the exact rounded contour of the canisterhousing 220, but substantially form a spade shaped configuration.

A circular shaped electrode 238 is illustrated in FIG. 23B.

A rectangular shaped electrode 246 is shown in FIG. 24A. Rectangularshaped electrodes 246 also incorporate electrodes that are substantiallyrectangular in shape. In particular to FIG. 24A, the corners of therectangular shaped electrode 246 are rounded. Moreover, one margin ofthe rectangular shaped electrode's conductive surface generally followsthe rounding of the distal end 246 of the canister housing 241.

A triangular shaped electrode 254 is depicted in FIG. 24B. Triangularshaped electrodes 254 also incorporate electrodes that are substantiallytriangular in shape. In particular to FIG. 24B, the corners of thetriangular shaped electrode 254 are rounded.

A square shaped electrode 257 is depicted in FIG. 24C. Square shapedelectrodes 257 also incorporate electrodes that are substantially squarein shape. In particular to FIG. 24C, the corners of the square shapedelectrode 257 are rounded.

An ellipsoidal shaped electrode 268 is depicted in FIG. 25A. The distalend of the ellipsoidal shaped electrode 268 generally follows theoutline of the rounded distal end 264 of the canister housing 260. Asthe ellipsoidal shaped electrode 268 moves proximally along the lengthof the canister housing 260, the conductive surface elongates and thenagain reduces in length to form a rounded proximal end. Similar to thethumbnail and spade shaped embodiments described above, the ellipsoidalshaped electrode's conductive surface is generally contained within thedistal end 264 of the canister housing 260. In alternate embodiments,the ellipsoidal shape electrode's conductive surface may extendproximally further within the canister housing 260. In yet anotherellipsoidal shaped electrode 264 embodiment, the margins of theellipsoidal shaped electrode's conductive surface refrain from followingthe exact rounded contour of the canister housing 260, but substantiallyform an ellipsoidal shaped configuration.

Energy emissions from any of the above described electrodes 204generally follow a path of least resistance. The intended pathway of theemission, therefore, may not necessarily be the pathway that theemission ultimately travels. This is particularly a problem withemissions made within the human anatomy where tissue conductivities arehighly variable. Obstructing, or low conductivity tissues like bonematerial, fat, and aerated lung may all redirect released energy awayfrom the heart. Alternatively, surrounding non-cardiac or striatedmuscle tissue, being generally a high conductivity tissue, may divertenergy emissions away from the heart. This is a particular concern forthe pectoralis, intercostal, and latissimus dorsus musculature, as wellas other thoracic, non-cardiac musculature found between the treatingelectrodes of the S-ICD. Since the S-ICD canister 190 of the presentinvention does not directly contact the heart muscle itself, such lowand high conductivity tissues will impede and/or shunt a percentage ofthe emissions from the present invention's electrode 204—permitting theheart to receive a fraction of the total emitted energy.

The present invention minimizes the effect of impeding and/orobstructing tissues by designing an electrode 204 and canister housing192 capable of focusing the electrode's array of emitted energy.Focusing the electrode's array of energy into a highly concentrated beamenables the resulting beam to be only minimally impeded or shunted awayby any surrounding bodily tissue. This focused array, therefore,delivers more of the originally emitted energy directly into themediastinum, and subsequently, into the intended heart muscle than wouldotherwise occur if the entire canister, or a majority of the canister,were electrically active—as is the case with standard transvenous ICDsystems. The present invention provides an electrode 204 and canisterhousing 192 design that creates a consistently focused array of energydirected toward the chambers of a recipient's heart.

Generally, it is desirable to have the electrode's longest conductivesurface plane positioned perpendicular to the extending ribs within arecipient's rib cage. Aligning the electrode 204 in this manner removesthe longest conductive plane from possibly extending directly over anyone particular rib. If the longest conductive surface were to extendalong the length of a rib, a greater percentage of emitted energy wouldbe distributed through the rib material, and consequently, may fail toreach the heart muscle. When aligned perpendicular to the ribs, only aportion of the conductive surface is directly over any particular rib.This alignment permits only a small percentage of the emitted energy tobe obstructed by the impeding rib material. Therefore, in particularS-ICD canister 190 embodiments that extend parallel with a recipient'srib cage, the width 205 of the electrode's conductive surface isapproximately greater than or equal to the length 207 of the electrode'sconductive surface. This electrode 204 sizing is best illustrated withreference to FIG. 20. The conductive surface of the thumbnail-shapedelectrode in FIG. 20 is depicted as both shallow and wide. In contrast,S-ICD canister 190 embodiments that extend perpendicular with arecipient's rib cage can have their conductive surface's length 207being greater than their conductive surface's width 205. The appropriateS-ICD canister 190 alignment, and subsequently the appropriate electrode204 alignment, is determined by the style of S-ICD canister 190 chosenfor the patient recipient. FIGS. 23A-26C illustrate numerous S-ICDcanister housing embodiments 192 for properly positioning an electrode204 over a recipient's heart. The embodiments depicted, however, are forillustrative purposes only, and are not intended to limit the scope ofthe present invention.

Another solution to the problem of thoracic tissues interfering withenergy delivery is by designing a canister housing 192 that may bestrategically positioned in close proximity to the patient's heart. Oneembodiment of the present invention possesses a curved canister housing192 that enables the S-ICD canister 190 to be advanced just over thepatient recipient's ribcage. Moreover, in another embodiment, thecurvature of the S-ICD canister 190 directly mimics the naturalcurvature of the ribcage.

Referring now to FIG. 21, the S-ICD canister 190 of FIG. 19 is shownfrom the side. FIG. 21 shows the S-ICD canister's top surface 194, thebottom surface 196 and the side 198 of the canister housing 192. In theembodiment depicted, both the top surface 194 and the bottom surface 196of the canister housing 192 are curved. In fact, throughout most of theproximal end 202 of the canister housing 192, the curvature is generallysimilar, and indeed can be identical, between the top surface 194 andthe bottom surface 196. In alternative embodiments of the presentinvention, the top surface 194 may be generally planar while the bottomsurface 196 is curved. In yet another embodiment of the presentinvention, the top surface 194 may be curved and the bottom surface 196is generally planar.

Referring back to the embodiment depicted in FIG. 21, the curvaturesbetween the top surface 194 and the bottom surface 196 are showndiffering toward the distal end 200 of the canister housing 192. At theS-ICD canister's distal end 200, the canister housing's top surface 194curvature tapers downwardly toward the canister's bottom surface 196.This tapering causes the distal end 200 of the canister housing 192 tobe narrower (of a decreased depth) than the canister's proximal end 202.In certain embodiments, this tapering in depth may be gradual throughoutthe length of the canister's housing 192, or alternatively, the taperingmay be confined to a particular area.

Tapering the depth of the canister housing 192 may improve the overallperformance of the S-ICD canister 190. In particular, a tapered distalend 200 may aid in insertion and advancement of the S-ICD canister 190within the patient recipient's body. A tapered distal end 200 enablesthe S-ICD canister 190 to easily traverse through narrow subcutaneousspaces. In particular, a physician generally tries to create apassageway into the patient's body that is appropriately sized for thecanister, especially in regard to positioning the distal segment of thecanister with the end containing the electrode in close proximity to thesternum. Tapering the distal end of the canister eliminates unnecessarytrauma to the patient in the tight spaces adjacent to the sternum. Forlarger canisters, however, this tight subcutaneous space is difficult totraverse. Subsequently, these larger canisters cause the physician toundertake extensive sharp and blunt dissection of the patient's tissuesin order to place the larger canister in the desired location.Regardless of the extent of the dissection, however, larger non-tapereddistal segments may prove extremely uncomfortable if forced into aparasternal position to satisfy the needs of focusing energy through themediastinum, and subsequently, to the patient's heart.

In contrast, embodiments of the present invention having narrow canisterhousings 192 may easily traverse such passageways. Moreover, taperingthe S-ICD canister's distal end 200 further streamlines the canisterhousing 192, and therefore, enhances the ease of the implantationprocedure. Tapering the S-ICD canister's distal end 200 is particularlyimportant when positioning the distal end of the canister housing asnear the left border of a patient's sternum as possible. This canisterhousing 192 placement optimizes energy delivery to the mediastinum, andtherefore, to the patient's heart.

The depth of the canister housing 192 is shown as being very narrow asto the canister housing's length 207. The canister's housing depth isless than approximately 15 millimeters. In alternate embodiments, thedepth of the canister's housing depth is approximately 5 millimeters toapproximately 10 millimeters. At the tapered distal end 200, thecanister housing may have a depth of approximately 1-4 millimeters.

In certain embodiments of the present invention, it is desirable toposition the S-ICD canister 190 in close proximity to the patientrecipient's heart, without directly contacting the heart. A favoredlocation for this S-ICD canister 190 placement is just over thepatient's ribcage. More particularly, in certain embodiments it isfavored to place the S-ICD canister 190 just to the left of, andadjacent to, the sternum with a segment at the distal end 200 containingthe electrode 204 closest to the sternum. FIG. 22 depicts the placementof the S-ICD canister 190 according to one embodiment of the presentinvention with the lead electrode traversing the subcutaneous tissueslaterally toward the axilla and then posteriorly to “catch” the currentas it is emitted from electrode 204 parasternally and anteriorly towardthe lead electrode 191 as it receives current exiting the posteriormediastinum and paraspinal tissues.

During the implantation procedure, a single incision 210 is made in theleft anterior axillary line approximately at the level of the cardiacapex, or around the fifth to the sixth intercostal space. The locationof this single incision 210 enables the physician to position both theS-ICD canister 190 and the canister's ancillary devices (e.g., pacingleads, shocking leads, etc.) from this single incision 210. Once thisincision 210 is made, the physician may insert surgical instruments or aspecially designed tool (not shown) through the incision 210 to shape apassageway for the S-ICD canister 190 to navigate. Although a tool maybe utilized in particular embodiments, a tool is not required—standardsurgical instruments, together with the general shape of the S-ICDcanister 190, are sufficient to facilitate proper positioning of thedevice in the left anterior thorax as adjacent as possible to thesternum.

In particular embodiments, a physician advances both the S-ICD canister190 and the lead electrode 191 within the patient to form adepolarization vector with respect to the patient's heart 218. Thedepolarization vector is a vector having an origin, a first end pointand a second end point.

In one embodiment, the origin of the depolarization vector originatesapproximately within the chambers of the patient's heart 218. Similarly,the first vector end point comprises the S-ICD canister electrode's 204positioning with respect to the patient's heart 218. Finally, the secondvector end point comprises the lead electrode's 191 positioning withrespect to the patient's heart 218. In alternate embodiments, the secondvector end point comprises a second canister electrode.

The lead electrode may be positioned at various positions within thebody because the length of the lead 193 may be varied. For example,S-ICD devices of the present invention may have leads with lengthsbetween 5 centimeters and 55 centimeters. Therefore, the S-ICD canister190 and lead electrode 191 of the present invention may create numerousdepolarization vectors.

In particular embodiments, a degree of separation of 180 degrees or lessexists between the S-ICD canister electrode 204 and the lead electrode191. In alternative embodiments, the degree of separation between theS-ICD canister electrode 204 and the lead electrode 191 is approximately30 degrees to approximately 180 degrees.

In order to obtain the desired degree of separation for thedepolarization vector, generally one device (either the S-ICD canister190 or the lead electrode 191) must be advanced anteriorly while theother device is advanced posteriorly from the initial incision 210.Accordingly, when the S-ICD canister 190 is advanced subcutaneously andanteriorly from the incision 210, the lead electrode 191 must beadvanced subcutaneously and posteriorly from the incision 210. With thisparticular embodiment, a physician may advance the S-ICD canister 190medially toward the patient's left inframammary crease to a locationproximate the patient's sternum 212.

Alternatively, the physician may advance, and subsequently position theS-ICD canister 190 within the anterior portion of the patient's ribcage216. This anterior placement may further include the patient's leftparasternal region, an anterior placement within the region of thepatient's third and the patient's twelfth rib 214, or generally anysubcutaneous ribcage 216 placement anterior to the patient's heart 218.In order to complement the S-ICD canister's 190 placement and obtain thecorrect depolarization vector, the lead electrode 191 must be advancedposteriorly toward the paraspinal or parascapular region of thepatient's ribcage 216.

In another embodiment of the present invention, the spatial positioningof the S-ICD canister 190 and the lead electrode 191, described indetail above, are reversed.

Referring back to FIG. 21, the curvature of particular S-ICD canisterembodiments 190 may be designed to generally mimic the natural curvatureof a patient's ribcage 216. These S-ICD canister embodiments 190restrict canister displacement and heighten comfort for the patientimplanted with the S-ICD canister 190. The anatomical shape of a patientrecipient's ribcage 216 varies. The present invention includes numerousS-ICD canister housing 192 curvatures to accommodate these varyingshapes. In particular, the present invention includes S-ICD canisters190 sized and shaped to properly fit children, as well as ones toproperly fit fully developed adults.

The curvature of the canister housing 192 is generally arc-shaped. Thedegree of curvature for any particular embodiment of the presentinvention is measured through a curvature vector theta (θ). Thecurvature vector θ is a vector having an origin 199, a first end pointand a second end point.

In one embodiment, the origin 199 of the curvature vector θ originatesapproximately at the center of the S-ICD canister 190 (lengthwise). Thefirst vector end point in this embodiment comprises the distal end 200of the S-ICD canister 190 and the second vector end point comprises theproximal end 202 of the S-ICD canister 190. In particular embodiments,the curvature vector θ possesses a degree of separation between 30degrees and 180 degrees. For example, a canister housing 192 having adegree of separation of 180 degrees is planar. Decreasing the degree ofcurvature θ causes the canister housing to become more arcuate in shape.

In alternative embodiments, the origin 199 of the curvature vector θ mayoriginate at a point other than the center of the S-ICD canister 190.Origins 199 shifted from the center of the S-ICD canister 190 produceregions of greater curvature, as well as areas of lesser curvature, inthe same S-ICD canister 190. Similarly, an S-ICD canister 190 maypossess multiple curvature vectors θ having origins 199 throughout thelength of the S-ICD canister 190. Multiple curvature vectors θ producevarious non-linear or nonsymmetrical curves that, in certaincircumstances, remain generally arc-shaped. Canister housings possessingmultiple curvature vectors θ are particularly suitable for S-ICDcanister 190 placement near the patient's sides (generally in the areaunder the patient's arms where the thorax has a more marked degree ofcurvature). Canister housings 192 incorporating a nonsymmetricalcurvature are generally longer S-ICD canisters 190 that span over thefront and sides of the patient's ribcage. In particular, these S-ICDcanisters 190 span areas of the ribcage 216 that are generally planar(around the patient's sternum 212), as well as areas that are highlycurved (generally in the area under the patient's arms).

Curved canister housings 192 are generally for S-ICD canisters 190 thatextend lengthwise, or approximately horizontally, along the length ofthe ribs in the ribcage 216. For certain embodiments, however, it isdesired to orient the length of the S-ICD canister 190 to beperpendicular to the length of the ribs in the ribcage 216. Aperpendicularly orientated S-ICD canister 190 generally requires verylittle, if any, curvature to conform to the ribcage 216.

FIGS. 23A-26C depict particular S-ICD canister 190 designs. In each ofthese particular S-ICD canister designs, the various materialconstructions, dimensions and curvatures, discussed in detail above, maybe incorporated within each individual S-ICD canister design.Furthermore, particular aspects of any individual S-ICD canister designmay be incorporated, in whole or in part, into another depicted S-ICDcanister design.

Turning now to FIG. 23A, an S-ICD canister 220 having a duckbill-shapedcanister housing 222 is shown. The duckbill-shaped canister housing 222has a proximal end 226 and a distal end 234. The proximal end 226 of theduckbill-shaped canister housing 222 further includes a main housingmember 228 and a distal housing member 230. The distal housing member230 is an elongated segment extending distally from the distal end ofthe main housing member 228. Although the two segments differ in theirsize and shape, the distal housing member 230 and main housing member228 are generally contiguously and fluidly attached to one another andmay be formed from a single mold. In alternative embodiments, however,the distal housing member 230 may be hinged to the main housing member228. The distal housing member 230 also generally comprises a materialthat is similar in composition to that forming the main housing member228. In alternate embodiments, however, the distal housing member 230may include a material that possesses enhanced electrically insulatedcharacteristics.

The main housing member 228 generally encases the operational circuitry,batteries and capacitors of the duckbill-shaped S-ICD canister 220. Thewidth and length of the main housing member 228 enable the main housingmember 228 to accommodate batteries and capacitors for delivering ashocking energy of approximately 50 J of energy, 75 J of energy, 100 Jof energy, 125 J of energy, 150 J of energy and 200 J of energy, forexample.

Although a specific number of batteries and capacitors are required fordelivering these charges, their positioning within the canister housing222 is highly modifiable. More specifically, the width of the mainhousing member 228 may be altered to accommodate a longer or shortercanister. For example, the width of the main housing member 228 may beincreased in order to obtain a main canister housing 228 of decreasedlength. Modification of the sizing and orientation of the main housingmember 228 allow manufacturers to create a variety of differing sizedduckbill-shaped S-ICD canisters 220. Increased specificity in thecanister housing's shape and size enhance the comfort and wearabilityfor the patient recipient.

In general, the width of the main housing member 228 is approximately 10cm wide or less. Likewise, the length of the main housing member 228 isapproximately 20 cm long or less. In particular embodiments the width ofthe main housing member 228 is 4 cm. In an alternative embodiment, thewidth of the main housing member 228 is 8 cm.

The distal housing member 230 is an elongated segment of canisterhousing that possesses a width that differs from that of the mainhousing member 228. The distal housing member's width decreases as thedistal housing member 230 extends distally. This tapering in widthresults in the formation of a shoulder region 232. In particularembodiments, the rate with which the width decreases as the proximalhousing member 230 extends distally is constant. In alternateembodiments, the rate is variable. A variable rate shoulder region 232taper proceeds at a rate of tapering where a unit of tapering width isnot directly related to a unit of length in the distal direction. Ineither of the embodiments, however, bilateral symmetry is maintainedthroughout the length of the distal housing member 230.

The shoulder region 232 is a generally rounded and smooth region of thecanister housing 222. As discussed in detail above, rounding the edgesalong the canister's surface enhances insertion of the S-ICD canister220. The rounded edges also reduce abrasion and inflammation associatedwith short-term and long-term wearability.

Extending distally beyond the shoulder region 232 is the distal head 234of the distal housing member 230. The distal head 234 is the distaltermination point of the duckbill-shaped S-ICD canister 220. The distalhead 234 includes a generally rounded end. In one embodiment,illustrated in FIG. 23B, the distal head 234 has a width greater thanthe width at a location within the shoulder region 232 of the distalhousing member 230. In alternative embodiments, the distal head's widthis equal to or less than the width at any point in the shoulder region232 of the distal housing member 230, as illustrated in 23A.

The length of the duckbill-shaped S-ICD canister 220 may depend highlyupon the shape and size of the distal housing member 230. In particularembodiments, the duckbill-shaped S-ICD canister 220 is approximately 30centimeters long or less. In alternative embodiments, theduckbill-shaped S-ICD canister 220 is approximately 10 centimeter orless. In particular embodiments, the length of the duckbill-shaped S-ICDcanister 220 may be curved, or alternatively, or a portion of the length(i.e., the shoulder region 232 and distal head 234) are curved.

The electrode 236 for the duckbill-shaped S-ICD canister 220 isgenerally seated within a portion of the distal housing member 230. FIG.23A diagrams in phantom the approximate location of an electrode 236 onthe duckbill-shaped canister housing 222. Although the electrode 236 isdepicted as generally circular in shape (in FIG. 23B), the electrode mayalso be “spade shaped” (depicted in FIG. 23A), thumbnail shaped, square,rectangular, triangular or ellipsoidal. The electrode 236 iselectrically coupled to the operational circuitry within the mainhousing member 228 of the S-ICD canister 220.

In certain embodiments of the present invention, an associated featureof the electrode 236 at the distal end is the presence of a margin ofinsulated material 237 around the active electrode 236. The margin ofinsulated material 237 may aid in directing emitted energy from theelectrode 236 inwardly toward the patient's heart instead of dispersingenergy outward toward the patient's chest wall. This margin of insulatedmaterial 237 typically ranges from 1-5 mm in width and may extend to themargin of the housing. Moreover, in certain embodiments, the margin ofinsulated material 237 comprises a ceramic material or other materialdesigned to facilitate focusing of current inward toward the heart.

In certain embodiments of the present invention, the electroniccomponents (e.g., circuitry, batteries and capacitors) of the S-ICDcanister 220 are generally absent from the distal housing member 230. Assuch, the depth of the distal housing member 230 may be greatly reduced.In these embodiments, a depth of approximately 1 millimeter may beobtained at the distal head 234 of the duckbill-shaped S-ICD canister220.

The duckbill-shaped distal housing member 230 enhances navigation duringcanister implantation. The distal head 234 of the distal housing member230 is blunt at its end to reduce trauma suffered to surrounding tissueduring the S-ICD canister's advancement or during chronic implantation.Similarly, the narrower distal head 234 (width-wise and depth-wise) iseasier to control during the advancement procedure. The smaller distalhead 234 also enables a physician to navigate the smaller and morecompact tissues adjacent to the sternum, which a larger head mightotherwise find unobtainable. Moreover, the narrower distal head 234 maybe advanced to a location in close proximity to the patient recipient'sheart 218 without concern of distorting or stressing the skin in theleft parasternal region.

The closer the electrode 236 is to the patient's heart 218, the lessenergy is required to achieve an adequate electric field or currentdensity to defibrillate the heart. A desirable anatomical position forreducing this energy requirement is just lateral to the sternum 212 ofthe patient. The area surrounding the patient's sternum 212 generallylacks a considerable accumulation of bodily tissue. Thus, subcutaneousS-ICD canister 190 positioning over the sternum 212, or some otherlocation just over the rib cage 216, provides a significant lessening ofthe required energy—due to proximity to the heart 218 and a reduction inimpeding surrounding tissue. Positioning an ICD canister of normalcontour in this area has proven difficult, however, and is additionallyaesthetically displeasing. The reduced profile of the duckbill-shapedS-ICD canister 220, however, provides such optimal electrode 236placement in a more aesthetically and less physically obtrusive manner.

Structurally, a reduction in the energy requirement frees space withinthe canister housing 222. This space was previously occupied bybatteries and capacitors needed for the higher energy requirements. Thisspace, however, is no longer required. The duckbill-shaped S-ICDcanister 220, therefore, can be smaller in length, width and depth.Eliminating batteries and capacitors also reduces the weight of thepresent invention. As described in detail above, reducing the weight ofthe S-ICD canister enhances patient recipient comfort.

FIG. 24A illustrates another embodiment of an S-ICD canister having agenerally rectangular-shaped canister housing 240. Therectangular-shaped canister housing 240 includes a top surface 241, abottom surface (not shown) and surrounding sides 248 connecting thesetwo surfaces. The rectangular-shaped canister housing 240 furtherincludes a distal end 242 and a proximal end 244. The electrode 246,shown in phantom, is generally positioned at either the distal end 242or the proximal end 244 of the canister housing 240. In alternativeembodiments, the rectangular-shaped canister housing 240 may include twoor more electrodes 246. When two electrodes are utilized, one electrodeis positioned at the distal end 242 of the canister housing 240 whilethe second electrode is positioned at the proximal end 244 of thecanister housing 240.

The length of the rectangular-shaped canister housing 240 isapproximately 30 centimeters long. In alternative embodiments, therectangular-shaped canister housing 240 is approximately 10 centimeterlong or less. The width of the rectangular-shaped canister housing 240is approximately 3 centimeters to approximately 10 centimeter wide.

FIGS. 24B and 24C depict additional embodiments of an S-ICD canisterhaving a generally square-shaped canister housing 250. The square-shapedcanister housing 250 includes a top surface 251, a bottom surface (notshown) and surrounding sides 252 connecting these two surfaces. Thesides 252 of the square-shaped canister housing are generally of thesame length. The electrode 254, shown in phantom, is generallypositioned in the center and to one side of the square-shaped canisterhousing 250. A triangular shaped electrode 254 is specificallyillustrated at the corner of the square-shaped canister housing 250 inFIG. 24B. In alternate embodiments, however, the electrode 254 may bepositioned toward the center of one of the sides 252 of thesquare-shaped canister housing 250, or at the center of thesquare-shaped canister housing 250, or rotated more. A square shapedelectrode 257 is specifically illustrated at the side of the canisterhousing 250 in FIG. 24C.

The length and width of the square-shaped canister housing 250 isapproximately 6 centimeters to approximately 8 centimeter long and wide.

FIG. 25A depicts yet another embodiment of an S-ICD canister having a“tongue depressor-shaped” canister housing 260. The tonguedepressor-shaped canister housing 260 includes a top surface 261, abottom surface (not shown) and surrounding sides 262 connecting thesetwo surfaces. The tongue depressor-shaped canister housing 260 furtherincludes a distal end 264 and a proximal end 266. The distal end 264 andthe proximal end 266 of the tongue depressor-shaped canister housing260, however, are rounded. In one embodiment, the rounded ends extendoutwardly away from the canister housing 260 in either the correspondingdistal or proximal direction. The rounded ends generally are circulararc-shaped curves; however, the rounded ends may also be elliptical ornonsymmetrical arc-shaped curves.

The electrode 268, shown in phantom, is generally positioned at eitherthe distal end 264 or the proximal end 266 of the canister housing 260.In alternative embodiments, the tongue depressor-shaped canister housing260 may include two or more electrodes 268. When two electrodes areutilized, one electrode is positioned at the distal end 264 of thecanister housing 260 while the second electrode is positioned at theproximal end 266 of the canister housing 260.

The length of the tongue depressor-shaped canister housing 260 isapproximately 30 centimeters long or less. In alternative embodiments,the tongue depressor-shaped canister housing 260 is approximately 15centimeter long or less. The width of the tongue depressor-shapedcanister housing 260 is approximately 3 centimeters to approximately 10centimeters wide.

Referring now to FIG. 25B, where a modified tongue depressor-shapedcanister housing 270 is shown. The modified tongue depressor-shapedcanister housing 270 is similar to the tongue depressor-shaped S-ICDcanister 260 depicted in FIG. 25A, however, the modified tonguedepressor-shaped canister housing 270 comprises only has a singlerounded distal end 272. The proximal end 274 of the modified tonguedepressor-shaped canister housing 270 is generally square.

FIGS. 26A-26C illustrate another embodiment of an S-ICD canister havinga multi-segment canister housing 280. The multi-segment canister housing280 includes at least two canister housing segments that are coupledtogether. The S-ICD canister depicted in FIGS. 26A, 26B and 26Cspecifically have a distal segment 282 and a proximal segment 284hinged, or otherwise coupled, together.

The distal segment 282 includes a top surface 292, a bottom surface (notshown) and surrounding sides 286 connecting these two surfaces. Thedistal most end 288 of the distal segment 282 comprises a roundedregion. An electrode 290 is disposed within this rounded region of thedistal segment 282 (shown in phantom). The electrode 290 generallyfollows the outline of the rounded region of the distal most end 288 ofthe canister housing, however, the electrode 290 may comprise of othershapes and sizes.

In an embodiment of the multi-segment canister housing 280, both theelectrode 290 and the electronics are disposed within the distal segment282. In alternative embodiments, the electrode 290 is disposed withinthe distal segment 282 and the electronics are located within theproximal segment 284 of the multi-segment canister housing 280.

FIG. 26B shows the distal segment 282 of the multi-segment canisterhousing 280 being curved to mimic the anatomical shape of a patientrecipient's ribcage 216. In the embodiment depicted, both the topsurface 292 and the bottom surface 294 of the proximal segment 282 arecurved. The curvature, however, differs at the distal most end 288 ofthe distal segment 282. At the distal segment's distal most end 288, thedistal segment's top surface 292 tapers downwardly toward the distalsegment's bottom surface 294. This tapering causes the distal most end288 of the distal segment 282 to be narrower than the distal segment'sdistal end 296. In certain embodiments, this tapering in depth may begradual throughout the length of the distal segment 282, oralternatively, the tapering may be confined to a particular area.

The proximal segment 284 also includes a top surface 298, a bottomsurface 300 and surrounding sides 302 connecting these two surfaces. Theproximal segment 284 depicted in FIG. 26B, however, is generally planar.In alternative embodiments, depicted in FIG. 26C, the proximal segment284 may also be curved and may also be of a different curvature to thatof the distal segment.

The length of the multi-segment canister housing 280 is approximately 30centimeters long or less. In alternative embodiments, the multi-segmentcanister housing 280 is approximately 20 centimeters or less. In yetanother embodiment, the multi-segment canister housing 280 isapproximately 12 centimeters or less. The width of multi-segmentcanister housing 280 is approximately 3 centimeters to approximately 10centimeters wide.

Numerous characteristics and advantages of the invention covered by thisdocument have been set forth in the foregoing description. It will beunderstood, however, that this disclosure is, in many aspects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size and arrangement of parts without exceeding the scope of theinvention. The invention's scope is defined, of course, in the languagein which the appended claims are expressed.

1. An implantable defibrillator comprising: a housing having a length ofabout 30 cm and having first and second ends with a first electrodedisposed on the first end and a second electrode disposed on the secondend; the housing containing operational circuitry configured to receivecardiac signals from the first and second electrodes and deliverdefibrillation energy via the first and second electrodes; the housingbeing shaped to allow implantation over the ribcage of a patient suchthat when the first end is disposed at a left parasternal location, thesecond end extends to underneath the patient's left arm; and the housingbeing configured to define a first curvature across a first region nearthe first end and a second curvature across a second region near thesecond end, the first curvature being generally planar and the secondcurvature being generally non-planar, such that the housing will conformto the contours of the ribcage when implanted subcutaneously.
 2. Theimplantable defibrillator of claim 1, wherein the housing has a width inthe range of about 3-10 cm.
 3. The implantable defibrillator of claim 2,wherein the housing is generally rectangular.
 4. The implantabledefibrillator of claim 2, wherein the first and second ends are roundedin generally circular arcs.
 5. The implantable defibrillator of claim 2,wherein the first end is rounded in a generally circular arc, and thesecond end is generally square.
 6. The implantable defibrillator ofclaim 1, wherein the housing is generally rectangular.
 7. Theimplantable defibrillator of claim 1, wherein the first and second endsare rounded in generally circular arcs.
 8. The implantable defibrillatorof claim 1, wherein the first end is rounded in a generally circulararc, and the second end is generally square.
 9. An implantabledefibrillator consisting of: a housing having a length of about 30 cmand having first and second ends with a first electrode disposed on thefirst end and a second electrode disposed on the second end; the housingcontaining operational circuitry configured to receive cardiac signalsfrom the first and second electrodes and deliver defibrillation energyvia the first and second electrodes; the housing being shaped to allowimplantation over the ribcage of a patient such that when the first endis disposed at a left parasternal location, the second end extends tounderneath the patient's left arm; the housing being configured todefine a first curvature across a first region near the first end and asecond curvature across a second region near the second end, the firstcurvature being generally planar and the second curvature beinggenerally non-planar, such that the housing will conform to the contoursof the ribcage when implanted subcutaneously.
 10. The implantabledefibrillator of claim 9, wherein the housing has a width in the rangeof about 3-10 cm.
 11. The implantable defibrillator of claim 9, whereinthe housing is generally rectangular.
 12. The implantable defibrillatorof claim 9, wherein the first and second ends are rounded in generallycircular arcs.
 13. A method of treating a patient comprising: making anincision in a patient's chest over the ribcage and developing asubcutaneous pocket for receiving an implantable device; implanting intothe subcutaneous pocket an implantable defibrillator comprising aphysiological sensor; and implanting into the patient a subcutaneouslead coupled to the implantable defibrillator, such that neither thelead nor the implantable defibrillator contact or enter the heart of thepatient and the heart is not exposed during the implanting steps. 14.The method of claim 13 wherein the physiological sensor is configured tomonitor the patient's blood glucose level.
 15. The method of claim 13wherein the physiological sensor is configured to monitor the patient'srespiration.
 16. The method of claim 13 wherein the physiological sensoris configured to monitor the patient's blood pressure.
 17. The method ofclaim 13 wherein the physiological sensor is configured to monitor thepatient's cardiac output.
 18. The method of claim 13 wherein thesubcutaneous pocket is placed such that the implanted defibrillator isat approximately the patient's left inframammary crease.